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Brachial Plexus & Upper Limb Nerve Injuries - NBE High-Yield Master Guide

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1. Brachial Plexus - The Framework (Memorize This First)

• Long thoracic nerve (C5-7) - serratus anterior - injury = winged scapula
• Dorsal scapular nerve (C5) - rhomboids + levator scapulae
• Suprascapular nerve (upper trunk, C5-6) - supraspinatus + infraspinatus

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2. Erb's Palsy (Upper Trunk Injury, C5-C6)

• Deltoid (abduction lost)
• Biceps (elbow flexion + supination lost)
• Supraspinatus/infraspinatus (external rotation lost)
• Wrist extensors (partially affected)

• Arm: adducted, internally rotated
• Elbow: extended (biceps paralyzed)
• Forearm: pronated
• Finger and hand movements are relatively spared (key distinguishing point)

"Erb palsy: affects C5-6 nerve roots. Common with vaginal delivery and traction-type injury, leading to adduction, internal rotation of the shoulder, inability to flex the elbow, wrist and digital flexion/extension intact. Over 90% have resolution at 3 months of age. Biceps function is the prognostic indicator." - Miller's Review of Orthopaedics, 9th Ed.

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3. Klumpke's Palsy (Lower Trunk Injury, C8-T1)

• All intrinsic hand muscles (thenar + hypothenar + interossei + lumbricals)
• Wrist and finger flexors (partially)

• MCP joints extended (intrinsics lost - cannot flex MCP)
• IP joints flexed (long flexors intact, unopposed)
• Thenar and hypothenar wasting
• Sensory loss on the medial arm, medial forearm, and ulnar aspect of the hand

"Lower type of brachial plexopathy (Déjerine-Klumpke type) results from injury to the eighth cervical and first thoracic roots or the lower trunk... When the first thoracic root is injured, the sympathetic fibers are interrupted. Therefore, an ipsilateral Horner syndrome (ptosis, miosis, and anhidrosis) results." - Localization in Clinical Neurology, 8th Ed.

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4. Radial Nerve Injury - Saturday Night Palsy & Humeral Shaft Fractures

A. Saturday Night Palsy (Axilla/Spiral Groove - Compression)

• Patient falls asleep drunk with arm draped over a chair back, or "honeymoon palsy" (arm draped over partner's shoulder)
• Compresses the nerve in the spiral groove
• Wrist drop (weakness of wrist extensors + finger extensors)
• If compression is at the axilla (e.g., improper crutch use): also get triceps weakness in addition to wrist drop

B. Humeral Shaft Fracture (Mid-shaft - ~22% incidence)

• The radial nerve is tethered in the spiral groove and is vulnerable to mid-shaft humeral fractures
• About 22% of humeral shaft fractures are associated with radial nerve injury
• Hallmark: wrist drop - weakness of hand and finger extensors
• Most are neuropraxias (stretching/compression, not transection) - spontaneous resolution reported in 60-92% of cases
• Management: splint wrist at ~60° of dorsiflexion while awaiting recovery; EMG at 6-8 weeks to assess axonal loss

"If you have a patient with a humeral shaft fracture, check the patient for wrist drop. Most radial nerve injuries are neuropraxias, or stretching of the nerve." - Schwartz's Principles of Surgery, 11th Ed.

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5. Anatomical Snuffbox

• Radial artery - passes obliquely through the floor (deep to tendons), adjacent to the scaphoid - pulse is palpable here
• Superficial branch of the radial nerve - passes subcutaneously over the roof
• Cephalic vein - origin from the dorsal venous arch crosses over the roof

• Up to 30-40% of scaphoid fractures are X-ray negative initially
• Missed/untreated scaphoid fractures → avascular necrosis of the proximal pole (the scaphoid's blood supply enters distally, so proximal pole depends on retrograde flow)
• Anatomical snuffbox tenderness: sensitivity 87-100%, specificity 3-98% - very sensitive, not specific
• Combination of ASB tenderness + scaphoid tubercle tenderness + scaphoid compression test: sensitivity 100%, specificity 74%

"When the hand is in ulnar deviation, the scaphoid becomes palpable within the snuffbox. This position enables the physician to palpate the bone to assess for a fracture." - Gray's Anatomy for Students

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6. High-Yield Extras Often Tested with This Group

Axillary Nerve Injury

• Fracture of surgical neck of humerus or glenohumeral dislocation
• Loses: deltoid (abduction) + teres minor (external rotation)
• Sensory loss: "regimental badge area" (lateral shoulder)
• Key distinguishing point: no biceps weakness (unlike C5 radiculopathy)

Long Thoracic Nerve (C5-C7)

• Serratus anterior paralysis
• Winged scapula - scapula protrudes when patient pushes against a wall
• Causes: mastectomy, stab wound, carrying heavy loads on the shoulder

Median Nerve - "Ape Hand" / Carpal Tunnel

• Recurrent branch lesion (at carpal tunnel): thenar wasting only, no sensory loss in palm
• Wrist-level cut: thenar wasting + sensory loss (lateral 3.5 fingers)
• High median nerve (elbow/above): add loss of FDP to index/middle + FPL = "hand of benediction" on attempted fist

Ulnar Nerve - "Claw Hand"

• At the wrist (most common): claw hand of ring + little fingers, hypothenar wasting, interosseous wasting, loss of sensation ulnar 1.5 fingers
• "All ulnar claws": the more distal the lesion, the more pronounced the claw (ulnar paradox)

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NBE Scenario Pattern Recognition

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FMGE Complete Coverage - Brachial Plexus & Upper Limb Nerve Injuries

What Was Already Covered vs. What FMGE Also Tests

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GAPS IN THE PREVIOUS ANSWER

1. The "Hand Postures" - FMGE Tests ALL of These by Name

• Claw hand is WORSE (more fingers affected) with a distal ulnar lesion than a proximal one - this is the Ulnar Paradox (explained fully below).
• Hand of benediction occurs when trying to MAKE A FIST (proximal median). Ulnar claw occurs at REST or when trying to EXTEND fingers.

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2. Median Nerve Injuries - Level by Level (Heavily Tested)

A. High Median Nerve (above elbow - supracondylar fracture in children)

• All forearm flexors except FCU and medial half of FDP (those are ulnar)
• FPL, FDP to index and middle (the AIN branch)
• Pronator teres, pronator quadratus
• LOAF muscles in the hand

• Hand of benediction when attempting fist (index + middle can't flex at DIP)
• Weak pronation
• Sensory loss: lateral 3.5 fingers + lateral palm
• Thenar wasting (with time)

B. Wrist Level Median Nerve (Carpal Tunnel Syndrome - CTS)

• Lumbricals 1 & 2 (index and middle finger MCP flexion)
• Opponens pollicis
• Abductor pollicis brevis (best single muscle to test)
• Flexor pollicis brevis (superficial head)

• Wrist flexion (FCR branches off proximal to tunnel)
• Sensation over thenar eminence (palmar cutaneous branch exits before the tunnel)
• Flexion of index/middle fingers at DIP (FDP branches off proximal)

• Tinel's sign - tapping over carpal tunnel at wrist reproduces tingling in fingers
• Phalen's test - forced wrist flexion for 60 seconds reproduces paresthesias (more sensitive than Tinel's)
• Reverse Phalen's (Prayer test) - dorsum of hands pressed together

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3. Ulnar Nerve Injuries - Level by Level

A. At the Elbow (Cubital Tunnel / Medial Epicondyle)

• FCU (ulnar wrist flexion - weak)
• FDP to ring + little (distal IP flexion lost - profundus to 4th and 5th digits)
• All interossei (abduction/adduction of fingers)
• Hypothenar muscles (ADM, FDM, ODM)
• Adductor pollicis + deep head FPB
• Lumbricals 3 & 4

• Claw hand (ring + little fingers) - MCP hyperextension + IP flexion
• Froment's sign - ask patient to hold paper between thumb and index finger; adductor pollicis is weak, so patient compensates by flexing thumb at IP (using FPL, which is median) to hold the paper. Positive = thumb IP flexes while gripping.
• Wartenberg's sign - little finger stays abducted (extended) during attempted adduction, because EDQ (radial nerve) is unopposed by 3rd volar interosseous (ulnar).
• Sensory loss: ulnar 1.5 fingers + medial palm + dorsum of ulnar hand (dorsal cutaneous branch exits ~5cm above wrist)

B. At the Wrist (Guyon's Canal)

• FCU and FDP to ring/little are spared (those branches come off above wrist)
• Motor-only deficit possible if deep branch alone is compressed (no sensory loss)
• If only deep motor branch: weak interossei + hypothenar + adductor pollicis, but no sensory loss

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4. The Ulnar Paradox (Direct FMGE MCQ)

• Claw hand results from paralysis of the lumbricals (which flex MCP and extend IP joints).
• In a HIGH ulnar lesion (at elbow): FDP to ring + little fingers is ALSO paralyzed. The FDP would normally pull the DIP and PIP into flexion - but without it, the fingers can't fully claw. The deformity is LESS prominent.
• In a LOW ulnar lesion (at wrist): FDP to ring + little is INTACT. So the fingers flex strongly at IP joints while the lumbricals are still out - giving a MORE pronounced claw.

"All ulnar claws: the more distal the lesion, the more pronounced the claw" - Miller's Review of Orthopaedics

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5. Radial Nerve - Posterior Interosseous Nerve (PIN) Syndrome

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6. Long Thoracic Nerve (C5-C7) - Winged Scapula

• Winging of scapula on pushing against a wall (medial border protrudes)
• Inability to raise the arm past 90° (glenoid can't rotate up)

• Mastectomy / axillary lymph node dissection
• Carrying heavy loads ("rucksack paralysis")
• Viral neuritis
• Stab wound

"Paralysis of the serratus anterior caused by damage to the long thoracic nerve produces a winged scapula on the affected side, making it impossible to raise the arm laterally past 90°" - Color Atlas of Human Anatomy, Thieme

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7. Musculocutaneous Nerve - Frequently Skipped

• Weak elbow flexion
• Weak forearm supination (biceps is the primary supinator)
• Loss of biceps reflex
• Sensory loss: lateral forearm (becomes the lateral cutaneous nerve of forearm after passing through biceps)

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8. Preganglionic vs. Postganglionic Brachial Plexus Injury

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9. Axillary Nerve - Complete Picture

• Loss of shoulder abduction (deltoid) - cannot abduct past 15-20°
• Loss of external rotation (teres minor)
• Sensory loss: "regimental badge area" - a circular patch on the lateral shoulder/upper arm

"Test sensation in the upper part of the lateral aspect of the arm ('regimental badge area'). Loss may indicate damage to the axillary nerve (following shoulder dislocation)." - Bailey and Love's Surgery, 28th Ed.

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COMPLETE FMGE QUICK-REFERENCE TABLE

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FMGE-SPECIFIC HIGH-YIELD POINTS NOT PREVIOUSLY COVERED

1. Radial nerve is the most common nerve injured in the upper limb overall (due to its vulnerability in the spiral groove).
2. Median nerve is the most commonly compressed nerve (CTS is the most common entrapment neuropathy in the body).
3. Ulnar nerve is the most commonly injured nerve at the elbow.
4. Supracondylar fracture of humerus in children = median nerve or AIN injury (the sharp distal fragment injures the anterior nerve).
5. Posterior dislocation of elbow = ulnar nerve injury.
6. Anterior dislocation of shoulder = axillary nerve injury.
7. Surgical neck of humerus fracture = axillary nerve injury.
8. Mid-shaft (spiral groove level) humeral fracture = radial nerve injury (22%).
9. Monteggia fracture (proximal ulna fracture + radial head dislocation) = PIN injury.
10. Colles fracture (distal radius) = median nerve / CTS (from hematoma or carpal distortion).
11. The only nerve that can regenerate at ~1 mm/day - spontaneous recovery is possible up to ~18 months from injury.
12. AIN test = "OK sign" - inability to form a circle = AIN palsy.
13. Froment's sign = adductor pollicis palsy (ulnar) - compensates with FPL (median).
14. Wartenberg's sign = 3rd volar interosseous palsy (ulnar) - little finger stays abducted.

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1. Brachial Plexus Framework - Roots→Trunks→Divisions→Cords→Branches table + pre-divisional branches
2. Erb's Palsy - Mechanism, muscles lost, waiter's tip posture, prognosis
3. Klumpke's Palsy - Mechanism, signs, Horner's association, Erb's vs Klumpke's comparison table
4. Radial Nerve - Axilla / spiral groove / PIN - with spiral groove vs PIN comparison table
5. Median Nerve - High level / AIN / CTS - level-by-level with comparison table
6. Ulnar Nerve - Elbow / wrist - with the Ulnar Paradox fully explained + comparison table
7. Other Key Nerves - Axillary, Long thoracic, Musculocutaneous
8. All 7 Classic Hand Postures - Named deformities table with mechanism
9. Preganglionic vs Postganglionic - Full comparison table (surgical implications)
10. Anatomical Snuffbox - Borders, contents, scaphoid fracture management
11. Fracture-to-Nerve Injury Mapping - 12-row table (direct FMGE favourite)
12. Master Quick-Reference Table - All nerves in one table
13. 28 FMGE One-Liners - Numbered list, exam-ready
14. Scenario Pattern Recognition - 18 clinical scenarios mapped to diagnosis

• From response 1 (NBE core): Erb's palsy, Klumpke's, radial nerve/Saturday night palsy, anatomical snuffbox - all fully covered in sections 2, 3, 4, and 10.
• From response 2 (FMGE gaps): Median nerve levels (high/AIN/CTS), ulnar nerve levels (elbow/wrist), ulnar paradox, PIN syndrome, axillary nerve, long thoracic nerve, musculocutaneous nerve, all hand postures, preganglionic vs postganglionic, fracture-nerve mapping, one-liners, and scenario recognition - all in sections 5–14.